Method of rolling metal



Patented May 19, 1936 UNITED STATES PATENT OFFICE METHOD OF ROLLING METAL No Drawing. Application November 21, 1934, Serial No. 754,183

Claims.

This invention relates to a method of rolling metal, and more particularly to the hot-rolling of sheet steels containing chromium (such as are usually identified as stainless steel) although 5 not limited thereto.

In the hot-roiling of sheet steels containing chromium, considerable trouble has been experienced due to the separation and consequently increased rate of cooling of the outer sheets of a pack. This condition causes the outer and inner sheets of the pack to elongate at different rates, frequently resulting in a lapping, or pinching, of the metal to form what are identified as pinchers and floppers. In addition, the inherent nature of the metal is such that if the sheets of a pack separate the outer ones, being colder, are liable to crack or break inwardly at the sides. This causes the intermediate, and more highly heated, sheets to have thickened edges.

In spite of the most careful handling during rolling, and the nicety of screw adjustment of the rolls of the mill, the packs will shift and air will enter thesheets thereof and oxidize the interior surfaces. This condition results in a scale which is not only difficult to remove but which is sometimes .sufli'ciently heavy to form surface defects, such as scale pits or what is known as rolled-in scale.

Stainless :steel sheets containing chromium in a range of between 11 percent and 30 percent (nickel-free) are rolled at lower temperatures (i. e., 1450 degrees to 1650 degrees Fahrenheit) than the chromium-and-nick-el bearing sheets (i. e., 18 percent chromium, 8 percent nickel, to 25 percent chromium, 12 percent nickel) which are necessarily rolled at temperatures of approximately 1800 degrees Fahrenheit and higher. In the hot-rolling of straight chromium-iron sheets, the lower rolling temperaturesnecessitate frequent reheating of packs to complete rolling togage. These reheatings must be more frequent if the sheets of .a pack separate (and hence lose heat at a greater rate) than would be the case if all of the sheets of the pack were maintained intact and lost heat at a uniform rate; similar to that of a single sheet of the same thickness as the pack.

It is one of the objects of the present invention to provide a novel method of rolling metal, and particularly sheet steels containing chromium, by the use of which the adjacent surfaces of sheets in pack form will remain intact when rolled at relatively low temperatures.

Another object is to provide a novel method of 55 the class described which will enable the processing of stainless steel in such manner that the several sheets of a matched pack will cool uniformly, and thus eliminate hot-mill defects which are identified as fioppers, pinchers, and the like.

A further object is the provision .ofa method of rolling metal, and particularly sheet steels containing chromium, by the practice of which that condition known as patching or partial settingup (that is to say, the partial separation thereof), will be completely eliminated, together with the reduction to a minimum of the oxidized ChlOr mium-iron scale, which minimized condition can be more readily removed by subsequent pickling operations.

A still further object is to provide a novel method of rolling metal which obviatesnumerous reheating steps with the result that chromiumbearing sheet metals may be hot-reduced in decidedly less time than heretofore possible.

A still further object is the provision of a meth- 0d of the class described which prevents cracks or broken edges, which occur on the outside sheets of a pack, together with the elimination of rolled-in scale, together with numerous other difficulties which have previously resulted from commercial methods now practiced, and particularly when processing extremely thin or light gages.

According to the teaching of the present invention, an adhesive medium or film is established between the adjacent surfaces of the chromium alloy steel sheets of the pack and causes them to become set to each other.

This setting-up of the sheets is the direct opposite of hot-rolling practice (known as loose rolling) on such sheets of low carbon deep drawing steel where means are provided (such as charcoal paste and the like) to prevent the sheets from adhering to each other. No attempts have ever previously been made to positively cause sheets to stick to each other, because ordinary carbon steels have a decided natural tendency in this direction.

The adhesive medium of the invention is essentially sodium silicate (water glass) and water in correct proportions although it may be used in powder or paste form and applied in any suitable manner, as long as it uniformly coats the about 1:5 (11 B.) to 123 (15 B.) respectively. These breakdowns may be of the chromium-iron class (17 per cent chromium, remainder iron) and are heated to a relatively low temperature, such as 1450 degrees Fahrenheit.

The term commercial solution of sodium silicate and water is intended to define a mixture of approximately 11 percent NazO (soda) and 31 per cent SiOz (silica), the remainder being water. This commercial solution of sodium silicate and water produces a high degree of adhesion of the sheets during hot rolling, and is at the same time of a consistency such as will permit ease and uniformity of application. Whilethe foregoing proportions are preferred, it is tobe understood that slight deviations therefrom may be resorted to without materially sacrificing the degree of adherence desired. However, a substantial variation will materially affect the degree of adhesion to the extent of actually acting as a separating medium instead of as an adhesive.

The pair is doubled when cold to form. four sheets in the pack and is then reheated and rolled to the correct gage. Usually, the finishing temperatures are such as to cause the sheets to be finished at a low or dark'temperature. Such a pack is so adherent or intact that it is free from air infiltration and hence relatively free from complex oxides. It acts as a single sheet of thickness equal to the thickness of the four sheets throughout the rolling and no undue precautions are necessary to see that screw pressures and other mill conditions are maintained within close limits. These alined' and adhering sheets are thus set-up so as to prevent loss of heat by the outside sheetsQ w The uniform heat of the pack means uniform elongation and consequently the absence of lapped'sections of metalwhich form pinchers, fioppers and the like.

"Actually 'efiective adhesion may be obtained over a wide range, from undiluted to more highly diluted solutions than that disclosed, which is,

however, the most effective working range to obtain effective adhesion, best sheet surface, and to avoid excessive sticking of finished packs which would make them. difficult to open. Such a pack, although closely adhering during its hot-rolling, is easily and readily opened and presents a smooth, dense surface. This is a very important factor for stainless sheets are, for the most part, later cold rolled, ground and highly polished, and with an initial smooth, dense surface such grinding and polishing operations are greatly reduced in time and expense. This is also a very important factor when highly finished surfaces are a prime consideration, such as cold-rolled-finished sheets produced by 4-high or 2-high cold rolling, with no other surfacing operation. v r

The sheets obtained by the practice of the present invention may be extremely easily pickled. Ordinarily, this pickling operation is a slow and tedious process involving an acid dip for about five minutes, followed by a caustic bath for about thirty minutes and then back to the acid'dip for another five to ten minutes, after which each sheet is scrubbed, rinsed and dried. Such a series of operations constitutes one complete cycle. Experiment has shown that the old method of hot-rolling produced complex chromium-iron oxides which often required as high as four or five such pickling cycles before they were clean. The present method enables the cleaning of stainless steel sheets in one cycle, which means fifty to seventy-five per cent saving of time and expense so far as the pickling operation is concerned.

The pack of sheets uniformly holds its heat throughout the rolling operation, but when finished is decidedly darker in color. Upon the pack being opened the sheets present a fine, smooth and dense surface, free from hot-mill defects such as pinchers and fioppers to the extent that the prime yield is raised from about sixty to over ninety per cent.

The sheets, if ground and polished to a high luster, are (by their basically smooth dense surface) processed in less time than heretofore. If cold-rolled finished, they have a better surface, free from scale pits and rolled-in scale.

While I have described one specific embodiment of my invention, it is to be understood that it may be applied with equal success to the hotrolling of numerous other metals and alloys, and that certain modifications and changes may be made without departing from the scope of the following claims.

I claim:

1. The method of rolling hot packs of metallic sheets containing chromium which includes applying an adhesive between adjacent surfaces of said sheets for setting up the pack during active hot rolling, said adhesive being composed of a mixture of sodium silicate and Water.

2. The method of rolling hot packs of metallic sheets containing chromium which includes heating the same to a temperature of between 1400 degrees to 1600 degrees Fahrenheit, and applying an adhesive between adjacent surfaces of said sheets for setting-up the pack during active hot-rolling, said adhesive being composed of between 5 to 15 per cent sodium silicate and 95 to per cent water.

3. The method of rolling hot packs of metallic sheets containing chromium which includes applying an adhesive between adjacent surfaces of said sheets whereby they are caused to adhere to each other and thus be set-up during active hot-rolling, said adhesive being composed of sodium silicate and water, the sodium silicate being composed of approximately one part NazO to 2.84 parts SiOz.

4. The method of rolling hot packs of metallic sheets which includes applying an adhesive between adjacent surfaces of said sheets whereby they are caused to adhere to each other and thus be set-up during active hot-rolling, said adhesive being composed of sodium silicate and Water, the sodium silicate being composed of approximately one part NazO to 2.84 parts S102.

5. The method of rolling hot packs of chromium-bearing metallic sheets which includes adhering adjacent surfaces of the sheets of said packs, and then rolling said packs whereby the relative movement of said sheets is prevented.

EDGAR MARBURG. 

